--Humphrey, the cat who launched a political scandal
Named the Prime Minister's Official Mouser in 1988, former stray Humphrey quickly became a fixture at 10 Downing Street, overseeing feline issues for Margaret Thatcher and John Major. But, when Tony Blair won the Prime Ministership in a landslide in 1997, Humphrey's position quickly became threatened. Rumors flew through the British press that Blair's wife hated cats and wanted Humphrey gone. And, when the aging cat was shipped off to a undisclosed retirement home a few months later, Blair's political opponents actually accused him of having Humphrey killed. Blair ended up having to bring political journalists to Humphrey's new home and allow them to photograph the cat—hostage style—with copies of that day's newspaper before his name could be cleared. The scandal is still remembered as the first major challenge of Blair's administration.

--Towser, the world's greatest mouser
Her position verified by the Guinness Book of World Records, it's fitting that Towser spent her 24 years surrounded by booze. The former official mouser to Scotland's oldest working distillery, Towser killed a reported 28,899 mice during her lifetime, earning both the Guinness mention and a commemorative bronze sculpture, which was dedicated at the factory after her death in 1987. Apparently, Towser's official number of kills was an average worked out by Guinness officials after observing her work over a period of days.

--Unsinkable Sam, World War II veteran
When the British Navy sunk the German battleship Bismarck in 1941, among the 115 survivors was the ships' cat, then named Oskar. Rescued by the British, Oskar was taken aboard the destroyer Cossack and lived there for five months, before that ship, too, was sunk. Oskar survived again. Transferred for a third time to the aircraft carrier Ark Royal, Oskar was on board (and survived) when the Royal was sunk a mere three weeks later. Rechristened "Unsinkable Sam," Oskar was sent to live out the rest of his life in a home for sailors, curtailing the career of what we can only imagine was one of Germany's most successful naval spies.